In mobile networks, such as a 3GPP (Third Generation Partnership Project) mobile network, various types of terminal devices may be used. For example, Machine Type Communication (MTC) terminal devices, such as sensor devices, alarm devices, remote control devices, or the like may be used in addition to conventional types of terminal devices, such as mobile phones, smartphones, data modems, mobile computers, or other types of UE. MTC terminal devices are typically characterized by a modest bit rate and sparse communication. MTC terminal devices may therefore be implemented with low-performance communication capabilities.
The existence of MTC terminal devices or other devices having similar data traffic characteristics may have an impact on the mobile network, in particular if the mobile network is designed to support large bandwidths or high throughputs, as for example in a mobile network according to 3GPP LTE (Long Term Evolution).
According to the Release 8/9 versions of the LTE specifications, the supported cell bandwidth is within the range of 6 and 100 resource blocks (RBs), about 1.4 to 20 MHz, and a UE is mandated to support all specified bandwidths in order to be standard compliant. Furthermore, UEs belonging to the lowest defined release 8/9 UE category need to support bit rates of at least 10 Mbit/s in the downlink and 5 Mbit/s in the uplink, which exceeds the needs of most MTC terminal devices. The ability to support high bandwidth, in particular bandwidth flexibility, and high throughput drives both cost and power consumption in the MTC terminal device. Accordingly, it is desirable to define low-performance UE categories in order to meet the characteristics of MTC terminals devices.
With the introduction of low-performance UE categories, it is possible to manufacture terminal devices with considerably less complexity and/or power consumption. In particular, the cost of each device is to a large extent driven by the silicon area. With significantly reduced throughput requirements, it is possible to reduce the size of hardware accelerators that are used to perform the most computationally complex operations, or even to replace them altogether with software implementations. Similarly, in a software-based implementation it is possible to replace large, possibly multiple, processors with smaller and/or fewer ones.
The potential to reduce the power consumption in a terminal device also strongly depends on the supported bitrates. Given a specific UE implementation, operation at the maximum supported bitrate requires a certain number of baseband processing operations, corresponding to a certain power consumption. Lower bitrates than the maximum one require fewer baseband processing operations, whether implemented in hardware or software. Consequently, support of lower bitrates may also be used for enabling reduction of energy consumption by the terminal device.
Even though it is possible to lower device complexity and/or power consumption when the throughput requirements are lower, there are typically still some timing constraints that need to be fulfilled in order to comply with a particular mobile network standard. For example, in 3GPP LTE one such timing constraint is associated with feedback messages of a retransmission protocol on the physical layer, which is used for reporting whether a data transmission has been successfully decoded by the UE or not. This timing constraint may actually limit how much simplified a particular implementation can be made, and/or how much the power consumption can be reduced. For example, a slower receiver processing at the terminal device may result in that the processing of a received data block has not yet terminated by the time that the next data block is being transmitted by the mobile network to the terminal device. In this case, terminal device may need to discard the transmitted data block, which reduces the efficiency of data transmission.
Accordingly, there is a need for techniques which allow for efficiently controlling transmission of data blocks between a mobile network and a terminal device.